OBJECTIVES: (1) Mechanisms involved in persistent infections of mosquito cells (and perhaps of whole mosquitoes) with togaviruses (Sinbdis and dengue-2) will be explored further with regard to: (a) "curing"; (b) time and rate of appearance of ts virus and its characterization; (c) question of a possible DNA transcript of viral genome (by transfection and hybridization). (2) Defective-interfering (DI) Sindbis virus and/or genomes will be analyzed further by hybridization and mapping on the whole viral RNA. (3) The reason(s) for "non-recognition" of DI particles by mosquito cells and their apparent failure to generate them under conditions leading to production of DI by vertebrate cells will be explored. (4) The cell-fusing agent (CFA) isolated from A. aegypti cell cultures will be further characterized, especially with regard to its possible relationship to LDH and similar viruses. (5) The methylation patterns of Sindbis viral, replicating, and DI RNA will be further analyzed. (6) Persistent infection of vertebrate and mosquito cells with dengue-2 virus will be investigated. (7) The mechanism(s) and specificity of dengue virus immune lysis will be studied. (8) The replication of dengue viral RNA and the morphogenesis of dengue-2 virus in different cells will be reexamined. BIBLIOGRAPHIC REFERENCES: Stollar, V., Shenk, T.E., Koo, R., Igarashi, A., and Schlesinger, R.W. Established mosquito cell lines and the study of togaviruses. Mtg. Invertebrate Tissue Culture, Mont Gabriel, Quebec, June 1975. (in press). Schlesinger, R.W. Sindbis virus replication in vertebrate and mosquito cells: An interpretation. In "International Symposium on Arboviruses", Helsinki, June 3-6, 1975. Medical Biology (in press).